A method presently used consists in fixing purlins on existing coverings between which is disposed in insulating material, and in fixing on said purlins a new covering.
According to another method also known, staples of U-shaped stirrups are fixed in the bottom of the corrugations, the rafters of the second covering being attached to said staples in order to prevent them from bearing against the corrugation apexes of the first covering.
Said known methods have disadvantages. In the first case, the purlins bearing on the corrugation apexes risk squashing the corrugations, due to the load thus applied at the apex of the deformable profiles. This is paticularly the case for coverings made of fibre-cement plates. On the other hand, the purlin fixation screws are large sized and work in flexion.
In the second case, the staples are not universal, the center distance of the axes of the staple fixation lugs being different according to the covering profile used (fibre-cement plate, corrugated sheet, etc.). Therefore, it is necessary to provide as many different staples as there are profiles currently used, which are presently several hundred in number. Moreover, the staples do not include means providing for the appropriate positioning of the purlins for their fixation, and when the positioning is reached, a drilling of the two parts (purlin and staple) has to be made in order to assemble them, for example with bolts. These drilling operations are very delicate to perform due to the inclination of the roofs.